Henderson B R, Menotti E, Kühn L C
Swiss Institute for Experimental Cancer Research (ISREC), Chemin des Boveresses 155, CH-1066 Epalinges s/Lausanne, Switzerland.
J Biol Chem. 1996 Mar 1;271(9):4900-8. doi: 10.1074/jbc.271.9.4900.
Iron regulatory proteins (IRPs) 1 and 2 bind with equally high affinity to iron-responsive element (IRE) RNA stem-loops located in mRNA untranslated regions and, thereby, post-transcriptionally regulate several genes of iron metabolism. In this study we define the RNA-binding specificities of mouse IRP-1 and IRP-2. By screening loop mutations of the ferritin H-chain IRE, we show that both IRPs bind well to a large number of IRE-like sequences. More significantly, each IRP was found to recognize a unique subset of IRE-like targets. These IRP-specific groups of IREs are distinct from one another and are characterized by changes in certain paired (IRP-1) or unpaired (IRP-2) loop nucleotides. We further demonstrate the application of such sequences as unique probes to detect and distinguish IRP-1 from IRP-2 in human cells, and observe that the IRPs are regulated similarly by iron and reducing agents in human and rodent cells. Importantly, the ability of each IRP to recognize an exclusive subset of IREs was conserved between species. These findings suggest that IRP-1 and IRP-2 may each regulate unique mRNA targets in vivo, possibly extending their function beyond the regulation of intracellular iron homeostasis.
铁调节蛋白（IRPs）1和2以同样高的亲和力与位于mRNA非翻译区的铁反应元件（IRE）RNA茎环结合，从而在转录后调节铁代谢的几个基因。在本研究中，我们确定了小鼠IRP-1和IRP-2的RNA结合特异性。通过筛选铁蛋白H链IRE的环突变，我们发现这两种IRP都能很好地结合大量类似IRE的序列。更重要的是，发现每个IRP都能识别一个独特的类似IRE靶标的子集。这些IRP特异性的IRE组彼此不同，其特征是某些配对（IRP-1）或未配对（IRP-2）环核苷酸发生变化。我们进一步证明了这些序列作为独特探针在人类细胞中检测和区分IRP-1与IRP-2的应用，并观察到在人类和啮齿动物细胞中，IRP受铁和还原剂的调节方式相似。重要的是，每个IRP识别IRE独特子集的能力在物种间是保守的。这些发现表明，IRP-1和IRP-2可能在体内各自调节独特的mRNA靶标，这可能将它们的功能扩展到细胞内铁稳态调节之外。
